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What is a glacier? “Glaciers are masses of ice and granular snow formed by compaction and recrystallization of snow, lying largely or wholly on land and showing evidence of past or present movement.” Matanuska Glacier, Alaska. Foto: Lachniet (1997)

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Basal Sliding Some glaciers move by slipping along basal water films Water source – Meltwater, geothermal and pressure melting – Not enough water – no sliding – Just right water – sliding – Too much water – development of subglacial drainage

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Subglacial Sediment Deformation As much as 90% of down- valley movement in some glaciers results from bed deformation Subglacial sediments are very wet with high pore water pressures (low effective stress)